1. Field of the Invention
The present invention relates to a broadcast receiving system and method for receiving a broadcasting radio wave and producing and outputting a video signal and an audio signal, as well as a medium which stores a broadcast reception control program.
2. Description of the Prior Art
Heretofore there has been known a broadcast receiving method wherein, with use of a broadcast receiving system in television, a broadcast radio wave in voice FM broadcast is received and is converted into an intermediate frequency signal, followed by amplification and detection to produce and output an audio signal. As this type of a broadcast receiving system there is known such a system as shown in a block diagram of FIG. 8. In the same figure, the broadcast receiving system roughly comprises a tuner IC 1, an SAW filter 2, a video intermediate frequency amplifier (VIF) circuit 3 and a detector circuit 4 both incorporated in a chroma IC, a VCO circuit 5, an SAW filter 6, a voice intermediate frequency amplifier (QIF) circuit 7, and a microcomputer 8.
The tuner IC 1, which is a frequency synthesizer type tuner, receives a broadcasting radio wave in television broadcast or voice FM broadcast, then converts it into an intermediate frequency signal and outputs the same signal, under control of the microcomputer 8.
The circuit which processes the intermediate frequency signal is a split carrier type circuit. In this circuit, the intermediate frequency signal passes through the SAW filter 2 when receiving television broadcast, while it passes through the SAW filter 6 when receiving voice FM broadcast. The SAW filters 2 and 6 are for removing a disturbance component from the intermediate frequency signal. But it is necessary that the frequency band for passage of the intermediate frequency signal be made narrower when receiving voice FM broadcast than when receiving television broadcast. For this reason the passing frequency band of the SAW filter 6 is set narrower than that of the SAW filter 2.
The intermediate frequency signal which has passed through the SAW filter 2 is subjected to intermediate frequency amplification in the VIF circuit 3 and is subjected to video detection in the detector circuit 4 in accordance with an oscillation frequency of an oscillation signal inputted from the VCO circuit 5, then is converted into an RGB signal. In the course of the intermediate frequency amplification there is produced a second voice intermediate frequency signal, which in the detector circuit 4 is subjected to amplification and FM detection into an AUDIO signal. As a result, an image is projected from a picture tube in accordance with the RGB signal and voice is outputted from a speaker in accordance with the AUDIO signal.
On the other hand, the intermediate frequency signal which has passed through the SAW filter 6 is subjected to intermediate frequency amplification in the QIF circuit 7 in accordance with the oscillation frequency of the oscillation signal inputted from the VCO circuit 5 and is inputted to the detector circuit 4, in which it is subjected to amplification and FM detection into an AUDIO signal. As a result, voice is outputted from the speaker.
There also is known such a broadcast receiving system as disclosed in JP-A No. 81034/1986. In this system, both a wide band pass filer and a narrow band pass filter which permits control of a resonance frequency according to channel selection are provided in a tuner portion and are used selectively. According to the construction disclosed therein, there is detected a displacement of carrier frequency from the output of a demodulation circuit and the resonance frequency is corrected in accordance with the detected displacement. According to the JP-A No. 81034/1986, both television broadcast and voice broadcast can thereby be received by a common tuner.
However, the above conventional broadcast receiving system involves the following problems.
In the former system, for the reception of voice FM broadcast it is necessary to separately provide an SAW filter and a voice intermediate frequency amplifier circuit. Besides, since it is necessary to let the pass band of the voice FM broadcast receiving SAW filter match the oscillation frequency of the oscillation signal outputted from the VCO circuit, it is impossible to use a general-purpose SAW filter and thus the freedom of circuit design is limited.
In the latter system, both television broadcast and voice broadcast can be received by a common tuner, but it is also required to let the pass band of the voice FM broadcast receiving SAW filter match the oscillation frequency of the oscillation signal outputted from the VCO circuit.